Importing/Exporting Calendars After Employee Retires

I had a user who retired after 40 yrs. and had created 3 shared calendars. How can I transfer ownership of these calendars to someone else? I have tried exporting and importing, which works except for being able to edit the appointment, because the organizer isn't the same anymore. So this raised another question of what happens with the resources. If a user books a resource and leaves, that resource stays tied up when it needs to be made available for another user. I am hoping for advice on setting up the calendars to avoid this problem.

we discourage employees from setting up shares using their own account unless it's for maybe a personal nature or something. We use one account as a central store to hold shared folders, calendars, and address books. this way they're not tied to an account of someone who might leave.